This application concerns a radically new and improved color television picture tube of the shadow mask variety. More particularly, this application is directed to lighthouse apparatus used to screen the faceplate of such a tube.
This unique tube alluded to has a construction quite different from conventional color cathode ray tubes. Conventional color cathode ray tubes have an envelope which comprises a funnel mated to a front panel having a deep, rearwardly extending flange. Mounted inside the front panel and carried on the rearward flange is a rigid mask-frame assembly. An electron gun assembly in the neck of the tube projects a plurality of electron beams through apertures in the mask whereupon the beams impinge a mosaic phosphor screen deposited upon the concave inner surface of the window portion of the front panel.
It is conventional to form the aforesaid mosaic phosphor screen by a photoscreening process which utilizes the mask as a photographic stencil in the deposition of the mosaic phosphor screen. Lighthouse apparatus used to accomplish the photoscreening typically comprises a table for supporting the front panel in a face down attitude with the shadow mask-frame assembly mounted therein. A light source contained in the bowels of the lighthouse irradiates a photosensitive coating on the concave inner surface of the viewing window through the apertures in the shadow mask. The photosensitive coating is then developed. By a series of exposures and developments, three interlaced patterns of red-emissive, blue-emissive and green-emissive phosphor elements are deposited as a mosaic on the inside surface of the viewing window. Another series of photoexposures and a development operation are required if the tube is of the type having a black matrix.
In order that the electron beams emitted by the gun assembly from the neck of the end product tube impinge mutually exclusively upon the phosphor elements they are designated to hit, it is important that the mosaic phosphor pattern, the shadow mask aperture pattern, and the electron gun assembly are all carefully positioned in the end product tube relative to each other.
To this end, during the photoscreening operations, the front panel is typically held in accurate position relative to the light source in the lighthouse by means of three precisely positioned bumpers which engage the outside surface of the front panel flanges at three points on the periphery of the front panel. These same bumpers are used as reference elements in the final tube assembly process.
The afore-described unique tube with which this invention is associated has an envelope comprising a flangeless, dished faceplate and a mating funnel whose mouth engages the concave rear surface of the faceplate. In the said unique tube, the shadow mask is suspended on the viewing window itself, on areas thereof outside the phosphor screen, by means of suspension devices in the corners of the faceplate. In the assembly of this novel tube, a unique system for referencing the faceplate to the funnel (and thus to the electron guns in the neck portion of the funnel) is employed. Rather than using external referencing means, as described, portions of the mask suspensions devices are internally referenced to integral provisions on the inside of the corners of the funnel mouth.
Because the referencing principles employed in the construction and manufacture of this unique tube are so different from those employed in the construction and manufacture of conventional tubes, and because the novel tube has so different a physical character, lighthouse apparatus used to screen conventional tubes is not suitable for use in the photoscreening of the faceplate of the said tube.